Add 'wait_for_previous' as an alias for the 'stonewall' option

Also update man page and HOWTO, plus add missing alias for
iomem_align while in there.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/fio.1 b/fio.1
index e48a16a..65877d2 100644
--- a/fio.1
+++ b/fio.1
@@ -630,7 +630,7 @@
 use.
 .RE
 .TP
-.BI iomem_align \fR=\fPint
+.BI iomem_align \fR=\fPint "\fR,\fP mem_align" \fR=\fPint
 This indiciates the memory alignment of the IO memory buffers. Note that the
 given alignment is applied to the first IO unit buffer, if using \fBiodepth\fR
 the alignment of the following buffers are given by the \fBbs\fR used. In
@@ -762,7 +762,7 @@
 \fBverify_backlog_batch\fR is larger than \fBverify_backlog\fR,  some blocks
 will be verified more than once.
 .TP
-.B stonewall
+.B stonewall "\fR,\fP wait_for_previous"
 Wait for preceding jobs in the job file to exit before starting this one.
 \fBstonewall\fR implies \fBnew_group\fR.
 .TP